Microcircuit fabrication requires that precisely controlled quantities of impurities be introduced into tiny regions of the silicon substrate. Subsequently, these regions must be interconnect to create components and ultimately VLSI circuits. The patterns that define such regions are created by a lithographic process. As semiconductor devices become more highly integrated, the line width of VLSI circuits typically are scaled down. The semiconductor industry's drive toward integrated circuits with ever decreasing geometries, coupled with its pervasive use of highly reflective materials, such as polysilicon, aluminum, and metal silicides, has led to increased photolithographic patterning problems. Unexpected reflections from these underlying materials, during the photoresist pattering process, result in the photoresist pattern being distorted.
This problem is further compounded when the photolithography is performed in the ultraviolet (UV) or deep ultraviolet (DUV) wavelength range. The resulting patterns generated in the photoresist are easily compromised by the effects of uncontrolled reflections from the underlying materials due to the increased optical metallic nature of underlying reflective materials at these wavelengths. Therefore, the fabrication of advanced integrated circuits with submicron geometries is limited.